This invention relates to heat exchangers and more particularly to plate type heat exchangers in which the plates are formed by pleat folding a single sheet of metal.
Plate type heat exchangers are commonly used for achieving an indirect heat transfer between two circulating fluids at different temperatures. These heat exchangers generally consist of a plurality of spaced parallel plates welded or otherwise attached between two end plates to define parallel passages. Manifolds are attached to the ends of the passages to direct each fluid to alternate passages so that each plate forms a heat conducting interface between the two fluids. Heat exchangers of this type are expensive to manufacture and present a risk of the two fluids mixing through leakage aroung the plates.
Improved versions of the plate type heat exchanger are shown, for example, in U.S. Pat. No. 2,945,680 which issued July 19, 1960 to Slemmons and U.S. Pat. No. 3,640,340 which issued Feb. 8, 1972 to Leonard et al. These patents disclose heat exchangers having a core formed from a single elongated sheet of metal which is pleat folded or folded back upon itself to form a continuous stack of interconnected parallel plates defining parallel passages. One advantage of this type of heat exchanger over the above-described individual plate heat exchanger is that side plates need not be sealed at two sides to prevent leakage between adjacent passages carrying different fluids since the folds in the metal form continuous side seals. However, there is some difficulty in accurately forming the folds and in maintaining proper spacing between the parallel sides of the passages. One method which has been suggested for accurately pleat folding an elongated sheet of metal for forming the core has been to use two spaced 90.degree. folds, thereby providing a square side to each passage. However, making two separate folds increases the manufacturing cost of the heat exchanger core. As to the spacing problem, the heat exchanger shown in U.S. Pat. No. 2,945,680 has a number of dimples or spacers formed in each metal sheet to maintain uniform spacings between adjacent sides of the folded sheet metal core. The heat exchanger shown in U.S. Pat. No. 3,640,340 has the core mounted in a manifold which has pockets formed along a side thereof for receiving and maintaining a proper spacing between each fold in the core. Still another problem with prior art heat exchangers of this type is in achieving the most efficient heat transfer between two circulated fluids. If the core is provided with substantially flat sides forming the walls of the internal passages, there will be a tendency for laminar fluid flow along the plates. Although the spacers or dimples in the heat exchanger of U.S. Pat. No. 2,945,680 will provide some turbulence to the fluid flowing through the heat exchanger, the turbulence is not sufficient to optimize heat transfer between the two fluids.